U.S. patent number 6,634,988 [Application Number 09/766,962] was granted by the patent office on 2003-10-21 for transmission shift control.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to Scott Thomas Kluemper, Jeffrey E Shultz.
United States Patent |
6,634,988 |
Shultz , et al. |
October 21, 2003 |
Transmission shift control
Abstract
A transmission control method comprises the steps of determining
whether a shift requiring an output shaft lock-up is commanded,
wherein such a shift involves a first torque transmitting mechanism
either being applied or released while a second torque transmitting
mechanism is held engaged. The control determines whether the
vehicle is stopped by one or all of the following: verifying the
vehicle service brakes are applied, the transmission output speed
is near zero, the engine speed is low, the oil sump temperature is
greater than a calibration temperature, and the turbine speed is
near zero if the vehicle is in forward drive. If the vehicle is
stopped, a lock-up torque transmitting mechanism is applied prior
to the shift operable to prevent torque transmission to the output
shaft. When the lock-up mechanism reaches capacity, the shift
proceeds by one of applying and releasing the first mechanism,
while maintaining the second mechanism engaged. Once the first
mechanism has one of reached capacity and released pressure below a
threshold, the lock-up mechanism is released to complete the
shift.
Inventors: |
Shultz; Jeffrey E (Zionsville,
IN), Kluemper; Scott Thomas (Monrovia, IN) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
25078065 |
Appl.
No.: |
09/766,962 |
Filed: |
January 23, 2001 |
Current U.S.
Class: |
477/116;
477/114 |
Current CPC
Class: |
F16H
61/0437 (20130101); F16H 61/0059 (20130101); F16H
3/66 (20130101); F16H 2061/0488 (20130101); F16H
2200/2043 (20130101); F16H 2200/201 (20130101); F16H
59/72 (20130101); F16H 61/686 (20130101); F16H
2061/0485 (20130101); F16H 2200/0052 (20130101) |
Current International
Class: |
F16H
61/20 (20060101); F16H 61/04 (20060101); F16H
59/72 (20060101); F16H 061/04 () |
Field of
Search: |
;477/116,117,97,114
;475/116,121 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Marmor; Charles A
Assistant Examiner: Ho; Ha
Attorney, Agent or Firm: Hodges; Leslie C.
Claims
What is claimed is:
1. A transmission control method comprising the steps of:
determining whether a shift requiring an output shaft lock-up is
commanded, wherein said shift involves a first torque transmitting
mechanism either being applied or released while a second torque
transmitting mechanism is held engaged; determining whether the
vehicle is stopped; if the vehicle is stopped, applying a lock-up
torque transmitting mechanism prior to the shift operable to
prevent torque transmission to the output shaft; when the lock-up
mechanism reaches capacity, proceeding with the shift by one of
applying and releasing the first torque transmitting mechanism,
while maintaining the second torque transmitting mechanism engaged;
then releasing the lock-up mechanism.
2. A transmission control method as defined in claim 1 wherein the
step of determining whether the vehicle is stopped further includes
the steps of: verifying a vehicle service brakes are applied;
verifying a transmission output speed is about zero; and verifying
an engine speed is about idle.
3. A transmission control method as defined in claim 2 wherein the
step of determining whether the vehicle is stopped further includes
the steps of: verifying the oil sump temperature is greater than a
calibration temperature; and verifying the turbine speed is about
zero if the vehicle is in forward drive.
4. A transmission control method as defined in claim 1 further
comprising the step of: proceeding with the shift by one of
applying and releasing the first torque transmitting mechanism
while maintaining the second torque transmitting mechanism engaged,
if the vehicle is not stopped.
5. A transmission control method as defined in claim 1 wherein the
step of applying the lock-up torque transmitting mechanism further
comprising the step of: adapting the lock-up torque transmitting
mechanism fill time and initial pressure from other transmission
shifts involving the lock-up torque transmitting mechanism to
ensure capacity is gained or released within a calibration time
period.
6. A transmission control method as defined in claim 1 further
comprising the step of: verifying the first torque transmitting
mechanism has one of reached capacity and released pressure below a
threshold, prior to releasing the lock-up torque transmitting
mechanism.
Description
TECHNICAL FIELD
The present invention relates to a shift control algorithm for an
automatic transmission.
BACKGROUND OF THE INVENTION
Automatic transmissions commonly employ a "clutch-to-clutch" shift
control strategy wherein the interchange between successive forward
ratios is accomplished by the disengagement of one of the torque
transmitting mechanisms and the substantially simultaneous
engagement of another torque transmitting mechanism. To accomplish
this strategy, pressure control devices such as pulse width
modulated (PWM) solenoids are driven by a transmission controller
to directly control oil pressure at the transmission torque
transmitting mechanisms.
The PWM signal may be modulated at a constant frequency (e.g. 102
Hz) with varying duty cycles to change oil pressure at the torque
transmitting mechanism. These pressure pulses generated by the
inherent operation of the PWM solenoid may, in certain
circumstances, result in torque spikes being transmitted from the
transmission to the vehicle driveline. Such torque spikes may
result in a poor shift feel or a shift noise or growl due to the
excitement of the driveline. The noise may be accentuated where the
transmission is installed in a light, stiff vehicle system. Further
the noise may be especially noticeable when the transmission output
shaft is stopped. The integration of a spring pack in the torque
transmitting mechanism or the addition of an accumulator to the
torque transmitting mechanisms feed circuit may reduce the effects
of torque spikes but at the expense of increasing system
content.
A means is needed to minimize the transfer of torque spikes
originating in the transmission to the driveline where it may lead
to dissatisfying customer shift noise or feel.
SUMMARY OF THE INVENTION
The present invention relates to a shift control algorithm for an
automatic transmission. In particular, the algorithm operates to
minimize torque spikes transmitted through the transmission by
locking the output drive shaft through the application of torque
transmitting mechanisms prior to a shift transition.
When such a shift is commanded, the algorithm verifies the vehicle
is effectively stopped prior to applying an output shaft lock-up
torque transmitting mechanism. Once the lock-up torque transmitting
mechanism reaches capacity, the shift may proceed by either
applying a torque transmitting mechanism to capacity or releasing
it to below a threshold pressure. The lock-up torque transmitting
mechanism is then released, completing the shift.
This shift control algorithm minimizes poor shift feel and noise.
It may be easily employed in an existing transmission without the
need for additional costly hardware and lead time.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a planetary gearing
arrangement;
FIG. 2 is a table of the torque transmitting mechanisms engaged for
each gear ratio; and
FIG. 3 is a flow chart of the shift control algorithm of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A planetary gearing arrangement is schematically represented in
FIG. 1. The arrangement has an input shaft 10, an output shaft 12
and three planetary gear sets 14, 16, and 18 disposed therebetween.
Five torque transmitting mechanisms are included where two are
represented as rotating clutches, first clutch C1, second clutch
C2, and three as stationary clutches or brakes, third clutch C3,
fourth clutch C4, and fifth clutch C5. The input shaft 10 is
drivingly connected to a drum 20 which drum 20 provides input
drives for clutches C1 and C2. The drum 20 is also drivingly
connected to a sun gear 26 of the gear set 18. The input shaft 10
is preferably driven by a conventional torque converter, not shown,
which is driven by an engine in a well known manner. The output
shaft 12 drives a driveline system 22 for transferring torque to
the vehicle wheels.
The first clutch C1 is connected to a shaft 28 which in turn is
connected to sun gears 30 and 32 of the gear sets 14 and 16
respectively. The second clutch C2 is connected to a shaft 34 which
is connected to a planet carrier 36 of gear set 16. The planet
carrier 36 is connected through a hub 38 to a ring gear 40 of gear
set 14.
The planetary gear set 14 also includes a planet carrier 42 on
which is rotatably mounted a plurality of pinion gears 44, only one
of which is shown, meshing with the sun gear 30 and ring gear 40.
The ring gear 40 is operatively connected to the fifth clutch C5,
which may be selectively engaged to restrain rotation of the ring
gear 40 and carrier 36. The planet carrier 42 is drivingly
connected to the output shaft 12, and thus the driveline 22.
The planetary gear set 16 further includes a ring gear 48 and a
plurality of pinion gears 50 rotatably mounted on carrier 36 and
meshing with sun gear 32 and ring gear 48. The ring gear 48 is
operatively connected to the fourth clutch C4 which may be
selectively engaged to restrain rotation of the ring gear 48.
The planetary gear set 18 includes a ring gear 54, a planet carrier
56 and a plurality of pinion gears 58, which are rotatably mounted
on carrier 56 and mesh with sun gear 26 and ring gear 54. The
carrier 56 is drivingly connected to a hub 60, which is connected
to ring gear 48. The ring gear 54 is operatively connected to the
third clutch C3, which may be selectively engaged to restrain
rotation of ring gear 54.
The stationary and rotational clutches C1-C5 are preferably of the
multiple disc type fluid-actuated torque transmitting mechanisms,
which are commonly used in planetary gear transmissions.
Alternatively, the stationary clutches may be band-type brakes. The
construction, operation, and control of these devices are well
known to those familiar with the art of power transmissions such
that a detailed description of these units is not considered
necessary.
The gearing arrangement may be controlled by the torque
transmitting mechanisms to provide six forward drive ratios and one
reverse drive ratio. The table of FIG. 2 illustrates the
combination of engaged torque transmitting mechanisms to establish
the drive ratios. First gear is established by the engagement of
the first clutch C1 and fifth clutch C5. Second gear is established
by the disengagement of the fifth clutch C5 and the substantially
simultaneous engagement of the fourth clutch C4. To establish third
gear, the fourth clutch C4 is disengaged as the third clutch C3 is
engaged. Fourth gear is established by disengaging the third clutch
C3 while engaging the second clutch C2. To establish fifth gear,
the first clutch C1 is disengaged as the third clutch C3 is
substantially simultaneous engaged. The sixth gear is established
by disengagement of the third clutch C3 and simultaneous engagement
of the fourth clutch C4. Reverse drive ratio is established by
engagement of the third clutch C3 and the fifth clutch C5. The
transmission is in neutral when only the fifth clutch C5 is
engaged.
It is apparent from the foregoing description of the drive ratios
that each ratio requires the engagement of different combinations
of two of the five torque transmitting mechanisms. Further, the
interchange between successive forward ratios is accomplished by
the disengagement of one of the clutches (the off-going clutch) and
the substantially simultaneous engagement of a second clutch (the
on-coming clutch) while maintaining another clutch engaged during
the transition.
A transmission electro-hydraulic control system, not shown,
operates to control the engagement and disengagement of the
clutches through the use of pulse width modulated solenoids and
shift valves as is well known in the art. The pulse width modulated
signal may be modulated at a constant frequency (e.g. 102 Hz) with
varying duty cycles to change oil pressure at a clutch. Under
certain conditions (e.g. warm hydraulic fluid, stiff driveline),
oil pressure modulated at a constant frequency may lead to
corresponding torque spikes transmitted through the transmission
output shaft to the drive system.
To minimize or even eliminate the transmittal of torque spikes to
the drive system 22 during a Neutral to Drive (N-D), or Drive to
Neutral (D-N) shift, the output shaft 12 may be "locked" from
rotation due to the application of a lock-up torque transmitting
mechanism. In the planetary arrangement described, the fourth
clutch C4, the output shaft lock-up mechanism, is applied, in
addition to maintaining engagement of the fifth clutch C5 during
these transitions. The fifth clutch C5 holds the ring gear 40 of
gear set 14, as well as the pinion gears 50 of gear set 16.
Engagement of the fourth clutch C4 holds the ring gear 48 of gear
set 16, which in conjunction with the held pinion gears 50,
restrict the sun gear 32 from rotation. Since the sun gear 32 is
restricted, the sun gear 30 of gear set 14 is also kept from
rotation. The end result is the planet carrier 42 of gear set 14 is
locked from rotation as is the transmission output shaft 12.
The present invention provides a shift control algorithm to
accomplish the task of locking the output shaft 12 under discrete
conditions as illustrated by the flow chart in FIG. 3. In block
100, the algorithm determines whether the transmission is being
commanded to shift from Neutral to Drive or Drive to Neutral. If
such a transition is commanded, the flow progresses to block 102
where it is determined whether the vehicle is effectively not
moving. This is important so that the output shaft 12 is not
abruptly stopped from rotating while the vehicle is in motion. In
order to meet the "vehicle is stopped" requirement, some or all of
the following criteria must be satisfied for a given time period:
a) service brakes applied, b) service brake status operational, c)
throttle near zero and valid, d) engine speed is low such as near
idle speed and valid, e) transmission output speed near zero, f)
turbine speed is near zero if in forward gear, and g) oil sump
temperature is greater than the calibration temperature and valid.
All of these conditions may be monitored by sensors currently
present in the vehicle.
If the vehicle is not stopped, then the standard first clutch
control is executed in block 104 without the output shaft lock-up
feature i.e. without engaging the lock-up fourth clutch C4 during
the shift. In the standard first clutch control transition from
Neutral to Drive, the first clutch C1 is the on-coming clutch and
the fifth clutch C5 is maintained engaged; there is no off-going
clutch. In Drive to Neutral shift, the first clutch C1 is the
off-going clutch, while the fifth clutch C5 is maintained engaged;
there is no on-coming clutch. In both instances the first clutch
transfers torque to the output shaft 12.
If the vehicle is stopped, then the output shaft is locked by
channeling apply pressure to the lock-up fourth clutch C4 during
the transition from N-D or D-N in block 106. The fourth clutch fill
time and initial trim pressure are based on adapted values from
other shifts which involve this clutch. In this instance for a N-D
shift, the time and pressure are based on the downshift from third
to second gear where the fourth clutch C4 is the on-coming clutch.
The fill time and initial pressure are adapted to ensure clutch C4
gains capacity with consistent timing. During the apply of the
fourth clutch C4, the pressure is ramped on for a calibration time
period. At the end of the calibration time period, pressure is
increased to a holding pressure and the clutch is referred to as
having capacity. In block 108, the control checks to see if the
fourth clutch C4 has reached capacity. If not, the apply state of
block 106 is continued.
When the fourth clutch C4 reaches capacity, control of the first
clutch C1 begins in block 110 while maintaining the clutch C4
engaged. In the transition from Neutral to Drive, the first clutch
C1 is the on-coming clutch and the fifth clutch C5 is maintained
engaged; there is no off-going clutch. In a D-N shift, the first
clutch C1 is the off-going clutch, while the fifth clutch C5 is
maintained engaged. In block 112, it is determined whether the
first clutch control is complete. For example, in a N-D shift, the
control is complete when the first clutch C1 has reached capacity,
whereas in a D-N shift, the control is complete when the clutch
apply pressure has dropped below a threshold pressure.
Once the first clutch control in block 112 is complete, either the
first clutch C1 has reached capacity or the pressure has dropped
below threshold, release of the fourth clutch C4 begins in block
114. The off-going pressure and time to release the fourth clutch
C4 are adapted from those experienced during downshifts from second
to first gear where the fourth clutch is the off-going clutch. The
fourth clutch pressure is step reduced to the initial off-going
pressure of a second to first shift, then the pressure is ramped
down at a calibration ramp rate. The pressures and times are
adapted to ensure the fourth clutch C4 consistently loses capacity
within a calibration time period. When the control algorithm is
completed, only the fifth clutch C5 is engaged in neutral and the
fifth clutch C5 and first clutch C1 are engaged for first gear.
The present invention provides a control method of locking the
transmission output shaft from rotation during the transition
between Neutral and Drive. This decouples the drive system from the
transmission and eliminates torque spike transmittal therebetween.
When such a shift is commanded, the algorithm verifies the vehicle
is effectively stopped before applying the lock-up torque
transmitting mechanism. Once the lock-up torque transmitting
mechanism reaches capacity, the interchange may proceed by either
applying an on-coming torque transmitting mechanism or releasing it
and disengaging the lock-up mechanism to complete the shift. With
the implementation of the control algorithm, customer
dissatisfaction due to noise and shift feel during the neutral to
drive transition may be substantially reduced.
The foregoing description of the preferred embodiment of the
invention has been presented for the purpose of illustration and
description. It is not intended to be exhaustive, nor is it
intended to limit the invention to the precise form disclosed. It
will be apparent to those skilled in the art that the disclosed
embodiment may be modified in light of the above teachings. The
embodiment was chosen to provide an illustration of the principles
of the invention and its practical application to thereby enable
one of ordinary skill in the art to utilize the invention in
various embodiments and with various modifications as are suited to
the particular use contemplated. Therefore, the foregoing
description is to be considered exemplary, rather than limiting,
and the true scope of the invention is that described in the
following claims.
* * * * *